Method for production of a magnetic-inductive flow meter

ABSTRACT

A method of producing a magnetic-inductive flow meter with at least one measurement tube, a magnetic field generating apparatus for generating a magnetic field which runs at least also perpendicular to the longitudinal axis of the measurement tube, and two measurement electrodes, the measurement tube having a metallic base body provided with a thermoplastic cover layer, a virtual connecting line of the two measurement electrodes running perpendicular to the direction of the magnetic field which is permeating the measurement tube perpendicular to the longitudinal axis of the measurement tube. The penetration sites of the measurement tube at which the measurement electrodes penetrate the measurement tube are easily made liquid-tight by a liquid-tight connection which has been produced by heating of the cover layer at the penetration sites for sealing the thermoplastic cover layer of the measurement tube to the measurement electrodes.

CROSS REFERENCE TO RELATED APPLICATION

This application is a division of commonly owned, co-pending U.S. patentapplication Ser. No. 13/946,253, filed on Jul. 19, 2013.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a magnetic-inductive flow meter, with at leastone measurement tube for through-flow of an electrically conductivemedium, with at least one magnetic field generating apparatus forgenerating a magnetic field which runs at least also perpendicular tothe longitudinal axis of the measurement tube, and with at least twomeasurement electrodes, the measurement tube having a metallic base bodyand the base body being provided with a thermoplastic cover layer atleast on the inside of the measurement tube, and the virtual connectingline of the two measurement electrodes running at least essentiallyperpendicular to the direction of the magnetic field which is permeatingthe measurement tube perpendicular to the longitudinal axis of themeasurement tube. The invention also relates to a method for producingsuch a magnetic-inductive flow meter.

2. Description of Related Art

Magnetic-inductive flow meters have been widely known in the prior artfor decades. Reference is made by way of example to the literaturecitation Technical Flow Rate Measurement by Dr. Eng, K. W. Bonfig, 3rdedition, Vulcan-Verlag Essen, 2002, pp. 123 to 167 and moreover to theliterature citation Principles of Magnetic-Inductive Flow RateMeasurement by Cert. Eng. Friedrich Hoffmann, 3rd ed., publication ofthe company KROHNE Messtechnik GmbH & Co. KG, 2003.

The basic principle of a magnetic-inductive flow meter for measuring theflow rate of a flowing medium goes back to Michael Faraday who suggestedthe use of the principle of electromagnetic induction for measuring theflow velocity of an electrically conductive medium as early as 1832.

According to the Faraday Induction Law, in a flowing, electricallyconductive medium which is permeated by a magnetic field, an electricfield intensity arises perpendicular to the flow direction of the mediumand perpendicular to the magnetic field. The Faraday Induction Law isused in magnetic-inductive flow meters in that, by means of a magneticfield generating apparatus which has at least one magnetic field coil,conventionally two magnetic field coils, a magnetic field which changesover time during a measurement process is generated and the magneticfield at least partially permeates the electrically conductive mediumwhich is flowing through a measurement tube. The generated magneticfield has at least one component perpendicular to the longitudinal axisof the measurement tube and perpendicular to the flow direction of themedium.

It was stated at the beginning that the measurement tube has a metallicbase body and the base body is provided with a thermoplastic cover layeron at least the inside of the measurement tube. Instead of such ameasurement tube, there can also be a measurement tube which, instead ofa metallic base body, has a nonmetallic base body, for example, aceramic base body. Here, magnetic-inductive flow meters will also beencompassed in which the measurement tube is formed entirely of athermoplastic material. But, it is always assumed below that themeasurement tube has a metallic base body and the base body tube isprovided with a thermoplastic cover layer on at least the inside of themeasurement. The formulation “at least on the inside of the measurementtube” of course also comprises an embodiment in which the base body isprovided on all sides with a thermoplastic cover layer.

With regard to the statement at the beginning that themagnetic-inductive flow meter under discussion includes at least onemagnetic field generating apparatus “for producing a magnetic fieldwhich runs at least also perpendicular to the longitudinal axis of themeasurement tube”, it is pointed out again here that the magnetic fielddoes run preferably perpendicular to the longitudinal axis of themeasurement tube and perpendicular to the flow direction of the medium,but it is sufficient that one component of the magnetic field runsperpendicular to the longitudinal axis of the measurement tube andperpendicular to the flow direction of the medium.

It was also stated at the beginning that the magnetic-inductive flowmeter under discussion includes at least two measurement electrodes, thevirtual connecting line of the two measurement electrodes running atleast essentially perpendicular to the direction of the magnetic fieldwhich is permeating the measurement tube. Preferably, the virtualconnecting line of the two measurement electrodes in fact runs more orless perpendicular to the direction of the magnetic field whichpermeates the measurement tube.

The electrical field intensity which is produced by induction in theflowing, electrically conductive medium can be measured by measurementelectrodes which are directly, therefore electrically in contact withthe medium as electrical voltage or also can be capacitively detected byelectrodes which are not directly, therefore not electrically in contactwith the medium. Here, it is a matter of magnetic-inductive flow metersin which the electrical field intensity produced by induction in theflowing, electrically conductive medium is measured by measurementelectrodes which are directly, therefore electrically in contact withthe medium as electrical voltage.

The measurement error in the magnetic-inductive flow meters known fromthe prior art is relatively small today; a measurement error less than0.2% can be accomplished.

For the known magnetic-inductive flow meters, reference is made by wayof example to the German patent disclosure document 197 08 857, 10 2004063 617 and corresponding U.S. Pat. No. 7,261,001, German patentdisclosure document 10 2008 057 755 and corresponding U.S. Pat. No.8,286,503, German patent disclosure document 10 2008 057 756 andcorresponding U.S. Pat. No. 8,286,502 and commonly owned, unpublishedpending U.S. patent application Ser. No. 13/687,313. The disclosurecontent of the aforementioned documents which were published beforehandare hereby expressly in corporate by reference in this patentapplication as is the substance of the co-pending U.S. patentapplication Ser. No. 13/687,313.

SUMMARY OF THE INVENTION

It was already stated above that, here, it is a matter ofmagnetic-inductive flow meters in which the electrical field intensityproduced by induction in the flowing, electrically conductive medium ismeasured by measurement electrodes which are directly, thereforeelectrically in contact with the medium as electrical voltage.Therefore, a primary object of the present invention is to devise amagnetic-inductive flow meter of the initially described type in whichthe penetration sites of the measurement tube, therefore the sites atwhich the measurement electrodes penetrate the measurement tube, can beeasily implemented in a liquid-tight manner, and to devise a method withwhich the above explained penetration sites can be easily implementedliquid-tight, therefore the measurement electrodes can be easilyimplemented liquid-tight, penetrating the measurement tube.

The magnetic-inductive flow meter of the invention in which theaforementioned object is achieved is, first of all, essentiallycharacterized in that at the penetration sites—sites at which themeasurement electrodes penetrate the measurement tube—a liquid-tightconnection which has been produced by heating of the cover layer isimplemented between the thermoplastic cover layer of the measurementtube and the measurement electrodes.

In the magnetic-inductive flow meter in accordance with the invention itis, first of all, important that the cover layer with which the basebody of the measurement tube is provided is also implemented within thepenetration sites. Therefore, reference to the base body being providedwith a thermoplastic cover layer at least on the inside of themeasurement tube is intended to include the fact that the thermoplasticcover layer extends out of the base body into the penetration sites. Asa result, it is not necessary for the thermoplastic cover layer to alsobe implemented on the outside of the measurement tube of the base body,even if it is considered advantageous and preferable for the measurementtube of the magnetic-inductive flow meter in accordance with theinvention that the base body be provided on all sides with athermoplastic cover layer, therefore this thermoplastic cover layer isprovided on the inside of the measurement tube of the base body, theoutside of the measurement tube of the base body and in the region ofthe penetration sites, the base body is therefore completely surroundedby the thermoplastic cover layer, therefore also in the region of thepenetration sites.

So that the measurement electrodes can be placed relatively easily inthe measurement tube, therefore can be inserted into the penetrationsites, the outside diameter of the measurement electrodes in the regionof the penetration sites is slightly smaller than the inside diameter ofthe penetration sites.

Otherwise, one preferred embodiment of the magnetic-inductive flow meterin accordance with the invention is characterized in that themeasurement electrodes have a collar which adjoins the measurement tubeon the outside and the measurement tube in the region of the penetrationsites has contact surfaces for the collar of the measurement electrodes.These contact surfaces are, first of all, helpful when the measurementelectrodes are placed in the penetration sites of the measurement tube.They are essentially used as a stop so that the measurement electrodescan be correctly placed by their being introduced into the penetrationsites of the measurement tube so far that the collar which lies outsidecomes into contact with the contact surface. Moreover, in thisembodiment, a liquid-tight connection is formed between the collar ofthe measurement electrodes and the contact surfaces which areimplemented on the measurement electrode in the region of thepenetration sites when the thermoplastic cover layer, as described asadvantageous above, completely surrounds the base body, therefore islocated not only in the region of the penetration sites, but also in theregion of the contact surfaces.

What was explained at the introduction and what was explained withreference to the object of the invention indicate that the subjectmatter of the invention is not only the above describedmagnetic-inductive flow meter, but also is a method for producing such amagnetic-inductive flow meter. That the production of themagnetic-inductive flow meter in accordance with the invention can alsohave special importance also results from what was stated above.

The method in accordance with the invention for producing amagnetic-inductive flow meter of the above described type is, first ofall, characterized essentially in that first the penetration sites whichare used for penetration of the measurement electrodes through themeasurement tube are placed in the base body of the measurement tube,preferably by drilling, that then the base body—in any case, in theregion of the penetration sites—is provided with a thermoplastic coverlayer and that finally the measurement electrodes are connectedfluid-tight to the measurement tube by heating the cover layer in theregion of the penetration sites.

In the second method step, the base body is provided, in any case, witha thermoplastic cover layer in the region of the penetration sites, andthis takes into account the fact that, on the one hand, thethermoplastic cover layer is critical to operation only in the region ofthe penetration sites, and on the other hand, that the thermoplasticcover layer can also be implemented on the inside of the measurementtube before the penetration sites which are used for penetration of themeasurement electrodes through the measurement tube are placed in thebase body of the measurement tube. However, preferably, first of all,the base body which is free of the cover layer is provided with thepenetration sites, and afterwards, the base body is provided completelywith a thermoplastic cover layer, therefore on the inside of themeasurement tube, the outside of the measurement tube, and, connectingthe inside of the measurement tube to the outside of the measurementtube, in the region of the penetration sites.

As the third method step, the liquid-tight connection of the measurementelectrode to the measurement tube was treated above, specifically by thestep of heating the thermoplastic cover layer in accordance with theinvention in the region of the penetration sites.

The latter described method step of the production of amagnetic-inductive flow meter in accordance with the invention can becarried out differently. One possibility is that the measurementelectrodes are heated to the temperature which is necessary for theconnection of the measurement electrodes to the cover layer of themeasurement tube, and then, preferably with a small penetration force,they are placed in the penetration sites. Another possibility ischaracterized in that the measurement electrodes are first placed in thepenetration sites, and when they have been placed in the penetrationsites, they are heated to the temperature which is necessary for theconnection of the measurement electrodes to the cover layer of themeasurement tube, preferably by inductive heating. The latter describedpossibility has the advantage over the first described possibility thathot articles, specifically preheated measurement electrodes, need not behandled.

A thermoplastic cover layer is critical for the magnetic-inductive flowmeter in accordance with the invention and critical for the method inaccordance with the invention for producing the magnetic-inductive flowmeter in accordance with the invention; the thermoplastic cover layer atleast partially, preferably completely covers the base body of themeasurement tube and melts on its surface when heated such that aliquid-tight connection is formed with the measurement electrodes inplace.

A suitable material for the thermoplastic cover layer is especially onewhich is sold under the trademark RILSAN®. The chemical name for thismaterial is polyamide 11. It is a powdered thermoplastic which isproduced on the basis of vegetable castor oil. In doing so, castor oilis processed into a monomer from which polyamide 11 is formed bypolymerization.

The advantages which have been achieved in accordance with theinvention, both in the magnetic-inductive flow meter in accordance withthe invention and also in the method in accordance with the inventionfor producing a magnetic-inductive flow meter, are mainly, especiallywhen it is considered that the magnetic-inductive flow meters inaccordance with the invention can be mass produced products, that in anespecially simple and economical manner a liquid-tight connection isachieved between the measurement electrodes which have been placed inthe measurement tube and the measurement tube. For liquid-tightconnection a special sealing means is not necessary, therefore forexample neither an O-ring nor complex screwing-in of the measurementelectrodes.

In particular, there are now various possibilities for embodying anddeveloping the magnetic-inductive flow meter in accordance with theinvention and the method in accordance with the invention for producingthis magnetic-inductive flow meter which will be apparent from detaileddescription of an exemplary embodiment of a magnetic-inductive flowmeter in accordance with the invention which is shown relativelyschematically in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a magnetic-inductive flow meter in accordancewith the invention in its basic assembly size,

FIG. 2 shows the measurement tube of the magnetic-inductive flow meteras shown in FIG. 1, in a schematic section,

FIG. 3 shows the measurement tube as shown in FIG. 2, in another sideview, also again in a section,

FIG. 4 schematically shows the cross section of the measurement sectionof the measurement tube as shown in FIGS. 1 to 3, in the region of themeasurement electrodes which are not shown, and

FIGS. 5 a & 5 b show, in views which have been enlarged compared to FIG.4, the cross section of the measurement section of the measurement tubeaccording to FIGS. 1 to 3 in the region of the measurement electrodes,with the measurement electrodes placed in the measurement tube.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows, only schematically, a magnetic-inductive flow meter 1 witha measurement tube 2 for the through-flow of an electrically conductivemedium, with a magnetic field generating apparatus 3 for producing amagnetic field which runs at least also perpendicular to thelongitudinal axis 4 of the measurement tube 2 and with two measurementelectrodes 5, 6, the measurement tube 1, both of which is only shown inFIG. 5, having a metallic base body 7 and the base body 7 being providedon all sides with a thermoplastic cover layer 8 and the virtualconnecting line 9 of the two measurement electrodes 5, 6 runningperpendicular to the direction of the magnetic field which is permeatingthe measurement tube 2 perpendicular to the longitudinal axis 4 of themeasurement tube 2.

In particular, the measurement tube 2 has an inflow section 2 a, ameasurement section 2 b which adjoins the inflow section 2 a, and anoutflow section 2 c which adjoins the measurement section 2 b.

In FIG. 1, it is only suggested that two hollow plates 3 a and twomagnet coils 3 b belong to the magnetic field generating apparatus 3.

It applies to the exemplary embodiment of a magnetic-inductive flowmeter 1 in accordance with the invention shown in the figures, as FIGS.1, 2 and 3 show, that the measurement tube 2 has a circular crosssection at the start of the inflow section 2 a and at the end of theoutflow section 2 c. In contrast, the measurement tube 2 in the regionof the measurement section 2 b has a more or less rectangular crosssection; this is shown by a comparison of FIGS. 1 and 2 on the one handwith FIG. 3 on the other, but mainly by FIGS. 4 and 5.

With regard to what is achieved by the geometry of the measurement tube2 which is shown in the figures, reference is made to co-pendingcommonly owned U.S. patent application Ser. No. 13/687,313.

As FIGS. 5 a and 5 b, show, a liquid-tight connection has been formed byheating of the cover layer 8 at the penetration sites 10—sites at whichthe measurement electrodes 5, 6 penetrate the measurement tube 2 in theregion of the measurement section 2 b—between the thermoplastic coverlayer 8 of the measurement tube 2 and the measurement electrodes 5 and6.

It noted that the outside diameter of the measurement electrodes 5, 6 inthe region in which they are located in the area of the penetrationsites 10 is slightly smaller than the inside diameter of the penetrationsites 10 prior to melting of cover layer 8.

Otherwise, FIGS. 5 a and 5 b show a preferred exemplary embodiment ofthe magnetic-inductive flow meter 1 in accordance with the invention tothe extent the measurement electrodes 5, 6 have a collar 12 whichadjoins the measurement tube 2 in the region of the measurement section2 b on the outside, and the measurement tube 2 in the region of thepenetration sites 10 has contact surfaces 13 for the collar 12 of themeasurement electrodes 5, 6. In the exemplary embodiment according toFIG. 5 b, the base body 7 has a continuously uniform wall thickness andthe cover layer 8 for implementation of the contact surfaces has asomewhat greater wall thickness. In contrast, it applies to theexemplary embodiment as shown in FIG. 5 a that the base body 7 has agreater wall thickness for implementing the contact surfaces 13 in thecorresponding region, while the cover layer 8 generally has a wallthickness which remains the same.

It applies to the production of the above explained magnetic-inductiveflow meter 1 in accordance with the invention that first the penetrationsites which are used for penetration of the measurement electrodes 5, 6through the measurement tube 2 are placed in the base body 7 of themeasurement tube 2, of course, in the region of the measurement section2 b, preferably by drilling, that then the base body 7—in any case inthe region of the penetration sites 10, but preferably entirely—isprovided with a thermoplastic cover layer 8, and that finally, themeasurement electrodes 5, 6 are connected fluid-tight to the measurementtube 2 by heating the thermoplastic cover layer 8 in the region of thepenetration sites 10.

The above explained third method step, the liquid-tight connection ofthe measurement electrodes 5, 6 to the measurement tube 2, can becarried out differently. One possibility is to heat the measurementelectrodes 5, 6, to the temperature which is necessary for theconnection of the measurement electrodes 5, 6 to the cover layer 8 ofthe measurement tube 2 prior to insertion, and then, preferably with asmall penetration force, to place the heated measurement electrodes 5, 6in the penetration sites 10. Another, and especially a preferredprocedure, is characterized in that the measurement electrodes 5, 6 arefirst placed in the penetration sites 10 of the measurement tube 2 andwhen they have been placed in the penetration sites 10, they are heatedto the temperature necessary for the connection of the measurementelectrodes 5, 6 to the cover layer of the measurement tube 2; this cantake place preferably by inductive heating.

What is claimed is:
 1. A method for producing a magnetic-inductive flowmeter having at least one measurement tube for through-flow of anelectrically conductive medium having a metallic base body having athermoplastic cover layer at least on an inside of the measurement tube,at least one magnetic field generating apparatus for generating amagnetic field which runs at least also perpendicular to thelongitudinal axis of the measurement tube and which permeates themeasurement tube perpendicular to a longitudinal axis of the measurementtube, and with at least two measurement electrodes, a virtual connectingline of the at least two measurement electrodes running at leastessentially perpendicular to the direction of the magnetic field,comprising the steps of: first, forming the penetration sites forpenetration of the measurement electrodes through the measurement tubein the base body (7) of the measurement tube, then, providing the basebody with a thermoplastic cover layer at least in a region of thepenetration sites, and then, connecting the measurement electrodes tothe measurement tube in a fluid-tight manner by heating thethermoplastic cover layer in the region of the penetration sites so asto by a heat seal the thermoplastic cover layer of the measurement tubeto the measurement electrodes.
 2. The method in accordance with claim 1,wherein the heating of the thermoplastic cover layer in the region ofthe penetration sites is performed by heating the measurement electrodesto a temperature necessary for the connection of the measurementelectrodes to the cover layer of the measurement tube and then placingthe measurement electrodes in the penetration sites.
 3. The method inaccordance with claim 1, wherein the measurement electrodes are placedin the penetration sites and wherein, after having been placed in thepenetration sites, the heating of the thermoplastic cover layer in theregion of the penetration sites is performed by the measurementelectrodes being heated to a temperature necessary for the connection ofthe measurement electrodes to the cover layer of the measurement tube 4.The method in accordance with claim 3, wherein the heating of themeasurement electrodes is performed by inductive heating.